Recently, diverse wireless communication technologies are under development in line with the advancement of information communication technology. Among them, a wireless local area network (WLAN) is a technique allowing mobile terminals such as personal digital assistants (PDAs), lap top computers, portable multimedia players (PMPs), and the like, to wirelessly access the Internet in particular service providing areas such as homes, offices, or aircraft based on a radio frequency technology.
The early WLAN technique supported the rate of 1˜2 Mbps through frequency hopping, spread spectrum, infrared communication, and the like, by using a 2.4 GHz frequency based on IEEE 802.11. Recently, the advancement of wireless communication technology allows supporting of a maximum rate of 54 Mbps by applying orthogonal frequency division multiplex (OFDM) technology and the like to the WLAN. Further, IEEE 802 has developed a wireless communication technique for improving quality of service (QoS), allowing compatibility of access point (AP) protocols, achieving security enhancement, making radio measurement or radio resource measurement, allowing wireless access in vehicular environment, ensuring fast roaming, establishing a mesh network, performing inter-working with external network, performing wireless network management, and the like, and put those techniques into practical use, or are still developing them.
In the WLAN system, a user equipment (UE), a non-AP station performs a scanning method to search for an accessible AP. The scanning method is a method for acquiring a list of candidate APs to be combined in a combining method, a follow-up method, and information about each AP.
The scanning method includes two types of method. A first scanning method is a passive scanning method which uses a beacon frame transmitted from an AP. In this method, a UE, which wants to become a member of a particular extended service set (ESS), receives beacon frames the APs periodically transmit to acquire a list of candidate APs transmitting beacon frames including the same service set ID (SSID) as the ID of the ESS to be connected and information about each candidate AP.
The second method is an active scanning method. In this method, a UE, which wants to become a member of a particular ESS, first transmits a probe request frame. The probe request frame includes an SSID to be connected. Respective APs receive the probe request frame, and if the APs have the same SSID as that included in the received probe request frame, they transmit a probe response frame to the UE. Accordingly, the UE can acquire a list of candidate APs based on the received probe response frames.
If, however, the UE is located in a hotspot, a list of candidate APs that can be acquired through the scanning method is so huge that overhead of the UE gradually increases in the scanning method. For example, in the passive scanning method, the number of scanned beacon frames including the same SSID as received is considerably increased to cause overhead. Also, in the active scanning method, the number of probe response frames with respect to the transmitted probe request frame is drastically increased, increasing overhead with respect to the scanning method as much.
However, with all the possibility of increasing overhead with respect to the scanning methods, information provided by the current scanning methods falls short of providing sufficient information regarding a network to be connected by the UE. In particular, with types of distribution systems (DSs) diversified, when the UE desires to access an external network, not the WLAN, to use services provided therefrom, the UE needs sufficient information about the access network (AN), but the current scanning methods fail to meet the need for the information about such DSs or AN.